This research concerns the electrically mediated fast block to polyspermy, a mechanism known to operate in fertilization of echinoderms, marine worms, and amphibians. The aims are to examine the generality and molecular basis of this electrophysiological regulation of sperm egg fusion. First, I will investigate whether the prevention of polyspermy in rabbits and fucoid algae involves an electrically mediated block. Second, I will investigate whether there might be a potential dependent sperm receptor in the egg cell membrane, or whether lipid bilayer fluidity might vary as a function of membrane potential: either of these factors might account for the potential dependence of sperm egg fusion. These studies will be done with eggs of sea urchins and fucoid algae, and will employ techniques of membrane biochemistry and biophysics. This research will add to our knowlege of fertilization and cell fusion.